Ziegler-Natta catalysts, which usually consists of compounds of Group IV-VIB metals and organometallic compounds of Groups I-IIIA of the Periodic Table of Elements, are widely utilized, in the polymerization of olefins. These catalysts are known to effectively promote the polymerization of olefins in high yield to form polymers that possess many desirable characteristics. However, the use of these conventional Ziegler-Natta catalyst systems are subject to important failings. Thus, new and improved catalysts are continually being sought.
Commonly in the polymerization of .alpha.-olefins a catalyst system having a magnesium halide support is utilized. Unfortunately, when polyolefins which are synthesized using such catalyst systems are processed into molded articles, the molding apparatus used in processing this polymer can be subjected to corrosion. This corrosion is caused by the presence of residual halide in the polymer product. More significantly, this adverse effect of corrosion is not limited to damaging just the molding apparatus. More importantly, the polymeric molded article processed by such corroded apparatus is often characterized as having undesirable aesthetic flaws.
The activity of a polymerization catalyst is defined as the weight of the polymer produced per weight of catalyst. Those skilled in the art are aware that the effect of higher activity not only reduces the amount of catalyst required for the polymerization process, but, more importantly, translates into lower catalyst concentration in the final polymeric product, usually resulting in a higher purity product.
One way of achieving higher catalytic activity without negatively effecting the physical characteristics of the polymer is to introduce co-catalysts or activators to the solid catalyst component during the polymerization process.
Typically, one skilled in the art adds one or more organoaluminum co-catalysts to the solid catalyst component during the polymerization of .alpha.-olefins. These co-catalysts are known to increase the activity of the polymerization catalyst without adversely effecting the physical properties of the resultant polymeric product.
U.S. Pat. No. 4,451,688 discloses a process for preparing a polyolefin wherein an olefin is polymerized in the presence of a catalyst system which comprises a solid component which is the reaction product of a magnesium-containing compound and a titanium and/or vanadium-containing compound. A second catalyst component is a silicon-containing compound having the structural formula R'.sub.m Si(OR").sub.n X.sub.4-m-n, where R' and R" are each hydrocarbon radicals having 1 to 24 carbon atoms; X is a halogen atom; m is 0 or an integer of 1 to 3; and n is an integer of 1 to 4. The catalyst system also includes a third catalyst component, an organometallic compound in which the metal of the organometallic compound is preferably aluminum or zinc.
U.S. Pat. No. 4,374,753 is directed to a solid catalyst component in which any one of a broad range of organic silicon compounds is disclosed on a silica or alumina support having surface hydroxyl groups. To this product is added an organomagnesium compound and an alcohol. The sequence of contact with the organomagnesium compound and the alcohol is random. The product of contact of these two components, independent of the sequence of their contact with the support, is reacted with a halide or alkoxide of titanium, vanadium, zirconium or mixtures thereof. The resultant solid catalyst component is employed with an alkyl or aryl aluminum co-catalyst to provide an olefin polymerization catalyst system.
U.S. Pat. No. 4,250,287 to Matlack relates to a solid catalyst component useful for polymerizing 1-olefins. The catalyst component is composed of a titanium halide deposited on an anhydrous magnesium halide-support and an activator component composed of a trialkylaluminum and an alkyl ester of an aromatic carboxylic acid. The productivity of the catalyst is increased by including a halosilane in the activator component.
U.S. Pat. No. 4,866,021 to Miro et al. provides a vanadium and a titanium-containing catalyst composition which produces high density, high molecular weight .alpha.-olefin polymers having a relatively broad molecular weight distribution. The catalyst component is produced by contacting a solid, porous carrier sequentially with a metal or a compound of a metal of Group IIB of the Periodic Chart of the Elements, e.g., a zinc compound, a halogen-containing aluminum compound, a vanadium compound and a titanium compound. The catalyst precursor is then combined with a suitable co-catalyst such as an alkyl aluminum compound and a halogenating agent. Suitable halogenated agents include methylene chloride, chloroform, carbon tetrachloride, dichlorosilane, trichlorosilane and silicon tetrachloride.
U.S. Pat. No. 4,831,000 to Miro is directed to a catalyst composition for the polymerization of olefins, particularly alpha-olefins. The composition is prepared by synthesizing a catalyst precursor and then combining it with a conventional catalyst activator. The precursor is synthesized by contacting a solid, porous carrier with an aluminum compound; contacting the resulting product with a mixture of vanadium and titanium compounds; contacting the product with an ether; and, pre-activating the product with a mixture of a halogenating agent and an aluminum compound. During polymerization, a halogenating agent may be used to obtain broad molecular weight distribution LLDPE and HDPE products. In another embodiment, the catalyst composition is used without a halogenating agent to obtain narrow molecular weight distribution HDPE and LLDPE products.
U.S. Pat. No. 4,912,074 to Miro, which is a continuation-in-part of U.S. Pat. No. 4,831,000 relates to a similar catalyst composition as U.S. Pat. No. 4,831,000; however, the pre-activating step has been omitted.
U.S. Pat. No. 4,972,033 to Miro relates to a catalyst composition for the polymerization of olefins. The composition is prepared by contacting a solid, porous carrier with an aluminum compound; contacting the resulting product with a mixture of vanadium and titanium compounds; contacting the product with an alkyl ether and, pre-activating the catalyst with a mixture of a halogenating agent and an aluminum compound. The catalyst is used without a halogenating agent in the polymerization medium to produce narrow molecular weight distribution HDPE and LLDPE products, or with a halogenating agent in the polymerization medium to produce broad molecular weight distribution LLDPE and HDPE products.
U.S. Pat. No. 5,006,618 to Miro, which is a divisional of U.S. Pat. No. 4,921,074 which was a continuation-in-part of U.S. Pat. No. 4,831,000, disclosed a catalyst composition for the polymerization of olefins, particularly alpha-olefins. The composition is prepared by contacting a solid, porous carrier with an aluminum compound; contacting the resulting product with a mixture of vanadium and titanium compounds; and, contacting the product with an ether. The catalyst composition is used with a conventional activator and, preferably, a halogensting agent in the polymerization medium to produce broad molecular weight distribution, high molecular weight HDPE or medium density, broad molecular weight distribution, high molecular weight resins which can be made into high strength films.